Salt and solute rejecting membranes suitable for use in desalination of aqueous solutions are the subject of numerous patents. Cadotte, U.S. Pat. No. 4,277,344 discloses permselective (salt rejecting) multi-layer membranes in which there is a microporous polysulfone substrate layer and a juxtaposed polyamide layer made from an aromatic triacid halide and an aromatic diamine. Scala et. al. U.S. Pat. No. 3,744,642 discloses multilayer membranes in which one layer is a porous substrate and the juxtaposed layer is a polyamide, a polyphenyl ester, or a polysulfonamide. Hara et.al. U.S. Pat. No. 4,353,802 discloses semipermeable composite membranes in which the membrane material is crosslinked using polyfunctional aromatic acid halides. Kamiyama et.al. U.S. Pat. No. 4,619,767 discloses permselective multi-layer membranes having a (1) microporous substrate layer (2) an ultra thin layer of a cross-linked polyvinyl alcohol/amino compound and (3) a porous inner layer of water insoluble polyvinyl alcohol located between the porous substrate and ultra thin layer. Other patents disclosing the preparation and properties of thin film composite membranes are U.S. Pat. Nos. 3,951,815; 4,005,012; 4,039,440 and 4,277,344.
A discussion of chlorine tolerance of reverse osmosis membranes of all types, be they anistropic or thin film composite is presented by Robert J. Petersen in a 1986 paper entitled "The Expanding Roster of Commercial Reverse Osmosis Membranes". It was stated in this report that thin film composite membranes in which the thin polyamide layer was composed of the reaction product of trimesoyl chloride and piperazine had the best chlorine tolerance up to that time for a polyamide TFC membrane, but that these might not be fully resistant to chlorine degradation despite the claims. These membranes are indeed not fully resistant to chlorine while membranes of the present invention are much superior in their resistance to this oxidant at normal operational hyperfiltration pH regions (or values). Thin film composite (TFC) membranes appear to the most efficient reverse osmosis (R.O.) membranes known today. These membranes are conveniently made by interfacial condensation polymerization to yield ultra thin films at the interface of an aqueous phase layer and a non-aqueous or organic (solvent) phase layer. Since the two phases are substantially immiscible, an ultra thin film will be generated at the interface of the two layers. Since the reaction is diffusion controlled and self limiting, the method yields ultra thin films, typically 50-5000 .ANG. thick (1 .ANG.=10.sup.-8 cm.).